Anticholinergics
AMBOSS-style class overview with comparison matrix, toxidrome, and DO/OMM correlates.
High-Yield Anticholinergic Toxidrome
"Blind as a bat, mad as a hatter, red as a beet, hot as a hare, dry as a bone, bowel and bladder lose their tone, heart runs alone."
Antidote: Physostigmine, a centrally acting acetylcholinesterase inhibitor that crosses the BBB. Atropine treats the muscarinic effects of organophosphate poisoning; pralidoxime is required for nicotinic flaccid paralysis.
Antidote: Physostigmine, a centrally acting acetylcholinesterase inhibitor that crosses the BBB. Atropine treats the muscarinic effects of organophosphate poisoning; pralidoxime is required for nicotinic flaccid paralysis.
Master Drug Comparison Matrix
| Drug | Selectivity / Target | Primary Indications | High-Yield Pearls & Traps | DO / Autonomic Correlate |
|---|---|---|---|---|
| Atropine | Non-selective (M1, M2, M3) antagonist | Bradycardia, organophosphate poisoning, pupil dilation | Mydriasis + cycloplegia; causes acute angle-closure glaucoma in shallow chambers | Sympathetic overdrive mimic; blunts vagal tone (CN X) |
| Scopolamine | Central & peripheral muscarinic antagonist | Motion sickness prophylaxis, end-of-life secretions | CNS sedation/amnesia; transdermal patch applied behind the ear | Vestibular ganglion modulation |
| Ipratropium / Tiotropium | M3 antagonist in bronchial smooth muscle | COPD, acute asthma | Quaternary amine (no CNS penetration); dry mouth; tiotropium is long-acting | T2–T7 viscerosomatic bronchodilation mimic |
| Oxybutynin / Tolterodine | M3 antagonist in detrusor muscle | Urge incontinence (overactive bladder) | Worsens delirium/dementia in elderly; urinary retention | T12–L2 sympathetic vs. S2–S4 parasympathetic balance |
| Benztropine / Trihexyphenidyl | Central M1 antagonist | Drug-induced parkinsonism, acute dystonia | Rebalances dopamine/acetylcholine in basal ganglia | Craniosacral & basal ganglia motor tracking |
| Glycopyrrolate | Peripheral muscarinic antagonist | Pre-op reduction of secretions, peptic ulcer | Quaternary amine; does NOT cross BBB (no delirium/CNS effects) | Autonomic salivary/gastric splanchnic block |
Receptor Second-Messenger Breakdown
- M1, M3, M5 → Gq → PLC → IP3 / DAG → ↑ Ca2+
- M2, M4 → Gi → ↓ cAMP
- M1: CNS, gastric parietal cells
- M2: SA/AV nodes, smooth muscle
- M3: Smooth muscle, glands, eye, bladder
- M4/M5: CNS
DO / Autonomic Correlates
- Cardiopulmonary: Sympathetic T1–T5 vs. vagus (CN X) parasympathetic. Anticholinergics remove vagal brake, producing tachycardia and bronchodilation.
- Bladder / Pelvic Splanchnics: Parasympathetic S2–S4 drives detrusor contraction; sympathetic T12–L2 inhibits it. M3 antagonists relax the detrusor.
- Contraindication: Avoid HVLA and osteopathic manipulative treatment in severe anticholinergic toxidrome with hyperthermia, delirium, or hemodynamic instability.